One of the problems associated with multivibrators is that its comparator switching transition level is very sensitive to changes in ambient temperature and power supply voltage. This change causes the multivibrator to have variations in the pulse duration time or oscillation frequency. To reduce this instability some form of compensation is necessary. One of the methods used is to use a FET as a resister to control the charging time of a capacitor. The FET resistance value is controlled by a temperature dependent voltage, which varies to maintain a constant capacitor charging time. This is described in U.S. Pat. No. 4,547,749 issued to Clinton Kuo. Another method is to use a constant current source circuit, which is designed to be temperature independent, to charge and discharge a timing capacitor. This is described in U.S. Pat. No. 4,714,901 issued to Jain et al.
In these methods the variation in pulse width or oscillator frequency has been reduced by controlling the charging time of capacitors, but nothing has been done to correct an other large error source, the comparator input offset voltage and its sensitivity to temperature and supply voltage change.